Textured optoelectronic devices and associated methods of manufacture

ABSTRACT

Textured optoelectronic devices and associated methods of manufacture are disclosed herein. In several embodiments, a method of manufacturing a solid state optoelectronic device can include forming a conductive transparent texturing material on a substrate. The method can further include forming a transparent conductive material on the texturing material. Upon heating the device, the texturing material causes the conductive material to grow a plurality of protuberances. The protuberances can improve current spreading and light extraction from the device.

TECHNICAL FIELD

The present disclosure is related to textured optoelectronic devices andassociated methods of manufacturing textured optoelectronic devices.

BACKGROUND

Optoelectronic devices source, detect and/or control radiation,including gamma rays, X-rays, ultraviolet and infrared radiation andvisible light. Examples of optoelectronic devices includeelectrical-to-optical or optical-to-electrical transducers, such aslight emitting diodes (“LEDs”), organic light emitting diodes (“OLEDs”),polymer light emitting diodes (“PLEDs”), and solar (photovoltaic) cells.Optoelectronic devices often include an electrode made from atransparent conductive oxide through which the radiation can pass.However, conductive oxide electrodes can reflect a portion of theradiation back into the device. This “lost” radiation can decrease lightextraction efficiency, waste energy, and reduce output. Accordingly,several improvements in light emission/absorption efficiency ofoptoelectronic devices may be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an optoelectronic devicein accordance with an embodiment of the technology.

FIGS. 2A-2C are schematic cross-sectional views of an optoelectronicdevice undergoing a process of forming a textured surface in accordancewith an embodiment of the technology.

FIGS. 3A and 3B are schematic cross-sectional views of optoelectronicdevices having solid state emitters (SSEs) in accordance withembodiments of the technology.

FIGS. 4A and 4B are schematic cross-sectional views of an optoelectronicdevice undergoing a process of forming a textured surface using a maskin accordance with an embodiment of the technology.

FIGS. 5A and 5B are schematic cross-sectional views of an optoelectronicdevice undergoing a pattern-transfer process in accordance with anembodiment of the technology.

DETAILED DESCRIPTION

Various embodiments of optoelectronic devices and associated methods ofusing and manufacturing optoelectronic devices are described below. Asused hereinafter, the term “optoelectronic device” generally refers todevices with semiconductor LEDs, PLEDs, OLEDs, laser diodes, solarcells/photovoltaic cells, or other types of solid state devices thatconvert between electrical energy and electromagnetic radiation in adesired spectrum. The terms “light emitting die” or “solid stateemitter” (“SSE”) includes LEDs, PLEDs, OLEDs, and other similar devices.Additionally, the term substrate refers to supports for individualoptoelectronic devices and larger wafers or workpieces upon which aplurality of optoelectronic devices are formed or mounted. A personskilled in the relevant art will also understand that the technology mayhave additional embodiments and that the technology may be practicedwithout several of the details of the embodiments described below withreference to FIGS. 1-5B.

FIG. 1 is a schematic cross-sectional view of an optoelectronic device100 in accordance with an embodiment of the technology. Theoptoelectronic device 100 includes an optoelectronic transducer 102, aconductive transparent texturing material 104 on the optoelectronictransducer 102, and a transparent conductive material 106 on thetransparent texturing material 104. In some embodiments, the transparenttexturing material 104 is titanium and the transparent conductivematerial 106 is Indium Tin Oxide (ITO). The transparent conductivematerial 106 includes a textured surface 110 having a plurality ofprotuberances 112 projecting away from the optoelectronic transducer102. The protuberances 112 can comprise a plurality of irregularpillars, spikes, and/or bumps, among others, in a random or undefinedpattern across the optoelectronic transducer 102.

In operation, radiation emitted from the optoelectronic transducer 102passes through the transparent texturing material 104 and the conductivematerial 106. Several embodiments of the optoelectronic device 100 withthe textured surface 110 are expected to increase light extraction andthe uniformity of current through the transducer 102. For example, thetextured surface 110 can reduce the loss of radiation to internalreflection, thereby increasing light extraction. In one simulation,light extraction efficiency for an optoelectronic device having anun-textured (generally planar) conductive material was approximately50%. Comparatively, for a device 100 having texturing/protuberances 112on the conductive material 106, light extraction efficiency wasapproximately 96%. These advantages are provided without losingfunctional area of the optoelectronic device 102.

The present technology further includes methods of manufacturingoptoelectronic devices having a conductive portion. For example, onemethod of forming a conductive portion on a substrate includes forming atitanium material on the substrate, forming a conductive material on thetitanium, and heating the conductive material. The conductive materialinitially has a first surface roughness before it is heated and a secondsurface roughness significantly greater than the first surface roughnessafter heating. One embodiment of this method is described in furtherdetail below with reference to FIGS. 2A-2C. Additionally, variations onthese methods and the resulting devices are described below withreference to FIGS. 3A-5B.

FIGS. 2A-2C are schematic cross-sectional views of an optoelectronicdevice 100 undergoing a process of forming the transparent conductivematerial 106 with the textured surface 110 in accordance with anembodiment of the technology. FIG. 2A shows the optoelectronic device100 after the translucent texturing material 104 has been formed, ordeposited, on an optoelectronic transducer 102 and the transparentconductive material 106 has been formed, or grown, on the texturingmaterial 104. As discussed above with reference to FIG. 1, in someembodiments the texturing material 104 is titanium and the conductivematerial 106 is ITO. In a particular embodiment, the conductive material106 is approximately 43.6% Indium, 2.9% Tin and 53.5% Oxide. In otherembodiments, the texturing material 104 and conductive material 106 areother materials through which radiation can pass. In one embodiment, thetexturing material 104 has a thickness ranging from about 20 angstromsto about 400 angstroms, and in a particular embodiment the texturingmaterial 104 has a thickness ranging from about 30 angstroms to about 60angstroms. In some embodiments, the conductive material 106 has athickness ranging from about 20 angstroms to about 4000 angstroms.

FIG. 2B illustrates the optoelectronic device 100 after the texturedsurface 110 has been formed on or otherwise imported to the conductivematerial 106. The textured surface 110 can be formed by heating thedevice 100, a portion of the device 100, or an environment in which thedevice is positioned, to a temperature from about 100° C. to about 600°C. In a particular embodiment, the device 100 is heated to a temperaturefrom about 350° C. to about 450° C. The inventors have discovered thatheating the conductive material 106 to such temperatures or in anenvironment of such temperatures with the texturing material 104 causesthe textured surface 110 to form (e.g., grow). In some embodiments, thetextured surface 110 takes the form of irregular, pillar-likeprotuberances 112 projecting away from the optoelectronic transducer102. The density and magnitude of the texturing (e.g., the size, shape,arrangement, and/or number of protuberances 112) can be sensitive to theheating temperature. After heating, the textured surface 110 of theconductive material 106 can have a texture or roughness that issignificantly greater than the roughness of the underlying texturingmaterial 104. Although only a single optoelectronic device 100 is shownin FIGS. 2A and 2B, the methods described herein can be performedsimultaneously or approximately simultaneously on multiple devicesacross a workpiece.

FIG. 2C illustrates the device 100 after a portion of a lens 252 hasbeen formed over the optoelectronic transducer 102. The lens 252 caninclude a transmissive material made from silicone,polymethylmethacrylate, resin, or other materials with suitableproperties for transmitting the radiation emitted by the optoelectronictransducer 102. The lens 252 can be positioned over the optoelectronictransducer 102 such that light emitted by the optoelectronic transducer102 passes through the lens 252. The lens 252 can include variousdiffusion features, such as a curved shape, to diffract or otherwisechange the direction of light emitted by the optoelectronic transducer102 as it exits the lens 252.

In selected embodiments, a converter material along and/or in the lens252 generates a desired color of light from the optoelectronictransducer. The converter material can include a phosphor-containingcerium (III)-doped yttrium aluminum garnet (YAG) at a particularconcentration for emitting a range of colors from green to yellow to redunder photoluminescence. In other embodiments, the converter materialcan include neodymium-doped YAG, neodymium-chromium double-doped YAG,erbium-doped YAG, ytterbium-doped YAG, neodymium-cerium double-dopedYAG, holmium-chromium-thulium triple-doped YAG, thulium-doped YAG,chromium (IV)-doped YAG, dysprosium-doped YAG, samarium-doped YAG,terbium-doped YAG, and/or other suitable wavelength conversionmaterials. In other embodiments, the converter material can be a remotephosphor separate from the lens 252, a direct phosphor in direct contactwith the optoelectronic transducer, or it can be absent altogether.

FIGS. 3A and 3B are schematic cross-sectional views of optoelectronicdevices 300 a, 300 b having solid state emitters (SSEs) 314 inaccordance with additional embodiments of the technology. FIG. 3A showsan optoelectronic device 300 a formed using methods generally similar tothose described above with reference to FIGS. 2A-2C. For example, atexturing material 104 is formed on an optoelectronic transducer 302,and a conductive material 106 is formed on the texturing material 104.As described above, the texturing and conductive materials 104, 106 canbe transparent materials. The conductive material 106 can be heated toform a textured surface 310 a having pillars or other types ofprotuberances 112 as described above with reference to FIG. 2B.

The SSE 314 can include a first semiconductor material 322, a secondsemiconductor material 326 and an active region 324 between the firstand second semiconductor materials 322, 326. In one embodiment, thefirst semiconductor material 322 is a P-type gallium nitride (GaN)material, the active region 324 is an indium gallium nitride (InGaN)material, and the second semiconductor material 326 is a N-type GaNmaterial. The first semiconductor material 322, active region 324, andsecond semiconductor material 326 can be deposited or otherwise grown orformed using chemical vapor deposition (“CVD”), physical vapordeposition (“PVD”), atomic layer deposition (“ALD”), plating, or othertechniques known in the semiconductor fabrication arts. The SSE 314 canfurther include a reflective material 320 formed between the substrate350 and the SSE 314.

In operation, as current flows from the first semiconductor material 322to the second semiconductor material 326, charge carriers flow from thesecond semiconductor material 326 toward the first semiconductormaterial 322 and cause the active region 324 to emit radiation. Theradiation propagates directly through the conductive material 106 orreflects off the reflective material 320 and passes back through thefirst semiconductor material 322, active region 324, and secondsemiconductor material 326. The radiation passes through the transparenttexturing material 104 and is transmitted through and refracted by theprotuberances 112. In other embodiments, the SSE 314 can take otherforms or arrangements that are known in the art.

FIG. 3B is a schematic cross-sectional view of an optoelectronic device300 b formed in a generally similar manner as the device 300 a shown inFIG. 3A, but varies from the device 300 a in that the texturing material104 has a non-planar outer surface 318. In the illustrated embodiment,the outer surface 318 includes ridges 334 and valleys 336. In otherembodiments, the first semiconductor material 322, the active region324, the second semiconductor material 326, the reflective material 320and/or the optoelectronic transducer 302 may additionally or alternatelybe uneven or patterned. A conductive material 106 is formed on the outersurface 318 of the texturing material 104 and can have a macro-profilecorresponding to the pattern on the outer surface 318. The contour ofthe texturing material 104 and the conductive material 106 can affectthe growth pattern of protuberances 112 on a textured surface 310 b ofthe conductive material 106. In the illustrated embodiment, for example,the protuberances 112 positioned over the ridges 334 generally extendfurther from the optoelectronic device 302 than do the protuberances 112positioned over the valleys 336. The ridge 334 and valley 336 patternshown in FIG. 2B is merely representative of one particular pattern forthe texturing material 104. A wide variety of different patterns orarrangements can be applied to the texturing material 104. In someembodiments, for example, the outer surface 318 can have a randomtexture, while in other embodiments the outer surface 318 can have apre-planned pattern of ridges 334 and valleys 336 that corresponds to adesired pattern of the resulting protuberances 112.

FIGS. 4A and 4B are schematic cross-sectional views of an optoelectronicdevice 400 undergoing a process of forming a textured surface 410 usinga mask 440 (identified individually as mask elements 440 a-440 c) inaccordance with an embodiment of the technology. FIG. 4A shows atransparent texturing material 104 that has been formed on anoptoelectronic transducer 102. The mask 440 is deposited and patternedto form the mask elements 440 a-440 c that define barriers over thetexturing material 104. In some embodiments, the mask 440 is made oftitanium nitride, but other materials may be used in other embodiments.

FIG. 4B shows the optoelectronic device 400 after a conductive material106 has been formed over the exposed portions of the texturing material104 and the mask 440. The conductive material 106 can be heated to growa textured surface 410 having pillars or protuberances 112 as describedabove with reference to FIG. 2B. The protuberances 112 grow over theexposed portions 442 of the texturing material 104, but not over themask 440. The planar portions 444 of the conductive material 106 thatoverlie the mask 440 remain generally un-textured. The mask 440,therefore, can be patterned on the texturing material 104 to selectivelyexpose portions 442 of the texturing material 104 where protuberances112 are desired.

Although the illustrated embodiment shows three mask elements 440 a-440c, in other embodiments the mask 440 can have a different arrangementand/or any number of mask elements on the surface of the texturingmaterial 104. The mask 440 can be configured depending on the intendedpurpose of the planar portion 444. For example, in some embodiments, themask 440 can be configured so that the planar portion 444 remainsgenerally flat for attaching bond pads (not shown) to the device 400. Inanother embodiment, the planar portion 444 can be used as a contactpoint for securing alignment of the device 400 on a substrate orelectronic device (not shown). In this example, the mask 440 can beapproximately the same size and have the same arrangement as thesecuring device contacts. In still another embodiment, the mask can beused to determine the selectivity of light absorption in a solar panelor cell.

FIGS. 5A and 5B are schematic cross-sectional views of an optoelectronicdevice 500 undergoing a pattern-transfer process in accordance with anembodiment of the technology. Referring to FIGS. 5A and 5B together, theoptoelectronic device 500 has been formed using methods generallysimilar to those described above with reference to FIGS. 2A-2C. Forexample, a texturing material 104 is formed on an optoelectronictransducer 102, and a conductive material 106 is formed on the texturingmaterial 104. As described above, the texturing and conductive materials104, 106 can be transparent materials. The conductive material 106 isheated to grow a textured surface 510 having pillars or protuberances112 described above with reference to FIG. 2B.

The protuberances 112 can be used as a mask to transfer the texturedpattern 510 to an underlying layer (e.g., the optoelectronic transducer102) of the device 500 by etching in the direction of arrow E.Specifically, various etching techniques, such as dry etching, can beused to remove all or a portion of the conductive material 106, thetexturing material 104 and/or the optoelectronic transducer 102. Byetching away a portion of the optoelectronic device 500, the irregularand/or random texture of the textured pattern can be transferred to theoptoelectronic transducer 102 without resorting to time- andchemical-intensive alternate techniques, such as photolithography or wetetching.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thedisclosure. For example, some of the embodiments described above showthe optoelectronic device as a SSE. However, other embodiments caninclude alternate devices described above, such as solar cells.Furthermore, some of the embodiments described above discuss usingtitanium and indium tin oxide for the conductive and texturingmaterials, respectively. However, in other embodiments, other materialsor compounds having similar characteristics, properties or functions canbe used. Many of the elements of one embodiment may be combined withother embodiments in addition to or in lieu of the elements of the otherembodiments. Accordingly, the disclosure is not limited except as by theappended claims.

We claim:
 1. A method for forming a solid state optoelectronic device,comprising: forming an optoelectronic transducer having at least a firstsemiconductor material, a second semiconductor material, and an activeregion between the first and second semiconductor materials; forming atitanium texturing material on the optoelectronic transducer; forming atransparent conductive material on the titanium texturing material,wherein forming the transparent conductive material comprises growing anon-uniform texture from the transparent conductive material, whereinthe non-uniform texture comprises a pattern; heating the transparentconductive material to produce a textured surface with a plurality ofprotuberances; and etching the transparent conductive material, thetitanium texturing material, and a portion of the optoelectronictransducer, thereby substantially transferring the pattern to theoptoelectronic transducer.
 2. The method of claim 1 wherein forming thetitanium texturing material comprises forming a titanium material havinga thickness from about 30 angstroms to about 60 angstroms.
 3. The methodof claim 1 wherein forming a transparent conductive material comprisesforming an indium tin oxide on the titanium texturing material.
 4. Themethod of claim 1 wherein the optoelectronic transducer comprises aphotovoltaic cell.
 5. The method of claim 1 wherein the optoelectronictransducer comprises a solid state emitter.
 6. The method of claim 1wherein forming the transparent conductive material comprises growingindium tin oxide on the titanium texturing material.
 7. The method ofclaim 6 wherein the indium tin oxide is grown at a temperature fromabout 100° C. to about 600° C.
 8. The method of claim 6 wherein theindium tin oxide is grown at a temperature from about 350° C. to about450° C.
 9. The method of claim 8 wherein the titanium texturing materialhas a thickness from about 30 angstroms to about 60 angstroms, and theindium tin oxide is grown at a temperature of about 400° C.
 10. Themethod of claim 1 wherein the protuberances are irregular pillarsprojecting away from the optoelectronic transducer.
 11. The method ofclaim 1 wherein the texturing material has a generally planar surfaceand the method further comprises: forming a mask on the texturingmaterial; patterning the mask to expose selected portions of thetexturing material where protuberances of the transparent conductivematerial are desired; and growing the transparent conductive material onthe mask and the exposed portions of the texturing material, wherein thetransparent conductive material is generally planar over the mask andthe transparent conductive material has protuberances over the exposedportions of the texturing material.
 12. The method of claim 1 whereinetching the transparent conductive material, the titanium texturingmaterial, and a portion of the optoelectronic transducer comprisesdry-etching.
 13. A method for forming a solid state optoelectronicdevice, comprising: forming an optoelectronic transducer; forming atexturing material on the optoelectronic transducer; forming aconductive material on the texturing material; heating the conductivematerial to produce a plurality of protuberances in the conductivematerial, wherein the plurality of protuberances form a pattern; andremoving the conductive material, the texturing material and at least aportion of the optoelectronic transducer via etching to transfer thepattern to the optoelectronic transducer.
 14. The method of claim 13wherein forming the texturing material comprises forming a texturingmaterial having a thickness from about 30 angstroms to about 60angstroms.
 15. The method of claim 14 wherein removing the conductivematerial, the texturing material and at least a portion of theoptoelectronic transducer via etching comprises removing the conductivematerial, the texturing material and at least a portion of theoptoelectronic transducer via dry-etching.